Azure gateway complete multipart ETag (#7500)

Compute md5 for azure multipart upload that matches s3 behavior
Reuse complete multipart md5 function in azure gateway

cmd/gateway-common.go

@@ -17,6 +17,7 @@
 package cmd
 
 import (
+	"context"
 	"net/http"
 	"os"
 	"strings"
@@ -349,6 +350,11 @@ func ErrorRespToObjectError(err error, params ...string) error {
 	return err
 }
 
+// ComputeCompleteMultipartMD5 calculates MD5 ETag for complete multipart responses
+func ComputeCompleteMultipartMD5(parts []CompletePart) (string, error) {
+	return getCompleteMultipartMD5(context.Background(), parts)
+}
+
 // parse gateway sse env variable
 func parseGatewaySSE(s string) (gatewaySSE, error) {
 	l := strings.Split(s, ";")